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EMM Procedure 4. Service Request
February 09, 2014 | By Netmanias (tech@netmanias.com)
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This document, as the fourth of the EMM Procedure series, will describe the service request procedure as defined as EMM Case 4 in our technical document, “Eleven EMM Cases in an EMM Scenario”. This procedure is used when a UE, initially attached to the network but staying inactive in Idle state, wishes to use LTE services again when there is new traffic. We will discuss how E-UTRAN resources are allocated to the UE again through this procedure, establishing an ECM connection (RRC + S1 signaling connections) in the control plane, and an E-RAB (DRB + S1 bearer) in the user plane. We will also look into how information elements in EPS entities are different before and after the procedure.
Page 1 of 6



1. Introduction


This document describes the service request procedure defined as EMM Case 4 in our technical document, “Eleven EMM Cases in an EMM Scenario” [1]. This procedure is performed when an inactive UE in Idle state wishes to get activated to handle traffic when there is new traffic. New user traffic can be uplink traffic from UE or downlink traffic from the network to UE. The UE’s E-UTRAN resources (allocated by eNB) have been released, and the UE has been in ECM/RRC-Idle state. Thus, in order for the UE to receive or send user traffic, DL or UL, it needs to transmit to ECM/RRC-Connected state through the service request procedure so that E-UTRAN resources can be allocated again.


This document explains the service request procedure in an LTE network.


Chapter 2 categorizes different cases of service request depending on where new traffic is generated.

Chapter 3 and 4 describe distinct procedures required in each service request case. Finally,

Chapter 5 summarizes how information elements in EPS entities are different before and after the procedure.




Page 1 of 6
Joseph 2014-04-21 08:04:47
Hi Netmanias,
I know, in the step "15) EPS Session Modification (optional)" in Figure 3, when P-GW forwards a CCR message to PCRF, IMSI and UE’s IP address are sent as well to inform whose session is sent. How does the P-GW know to which user the session belongs to when no user ID is included in the Modify Bearer Request message that S-GW is sending to the P-GW?
Netmanias 2014-04-21 16:39:46
Hi Joseph,

In control plane, there is a GTP-C tunnel (per user) established between S-GW and P-GW. This tunnel (or user of this tunnel) is identified by a TEID. The TEID value is carried in the GTP tunnel header while control message is carried in the GTP tunnel payload field.

In the Step 15), when S-GW sends a Modify Bearer Request message to P-GW through this GTP-C Tunnel, the P-GW checks the TEID in the tunnel header and learns whose session it is.
debasish 2014-05-27 16:16:03
Hi Netmanias team,

Please explain me a scenario where UE is establishing a second dedicated bearer(ofcourse network initiated).
gecuili 2015-01-26 17:34:14

 “At this time, the eNB allocates eNB UE S1AP ID, and includes it in the Initial UE Message sent to the MME. ”

eNB UE S1AP ID --》 eNB S1AP UE ID. Right?


azgar shaik 2015-03-22 13:40:35

Is there Any Timer defined for Inital Context Setup Request/ Response?

James 2015-06-23 21:14:29

"SGW finds out at which MME the UE is registered"  how?

Ranjith Kumar Kopperla 2015-12-14 18:51:18

Dear Netmanias team,


Thanks for your explanation, can you please explain what happens when the Service Request procedure is rejected. If possible please explain the behavior for different cause codes.



nitinatakg@gmail.com 2016-03-11 14:39:42

This site is the best

Gul 2016-06-24 12:13:50

I have a question , After establishing the internet connection Ue is sending SR for three times since Network is ignoring the Service request . But according to spec it should send for five times .

What could be the reason here ?

Harshil 2017-10-09 18:53:59

Great Explanation with a diagram

rajeevkr 2017-10-14 00:38:04


Could you please explain when this scenario happens: After the S1 Setup Procdure between eNB and MME UE is sending Service Request(RRC Connection Request cause Mo-Data) and being rejected by MME since UE didn't do an Attach Request. UE never attached before.

Bhoop Singh 2020-12-16 03:21:41

How S-GW knows that the incoming data is for which MME/UE, means how S-GW decides the MME to send the DL data Notification. Please expaln thanks in advance

vimal kumar mishra 2021-02-12 16:04:00

What kind of information related to UE subscription is kept in SPR ? Why PCRF does not use HSS for the same purpose ? 

Irfan Ali 2021-06-06 18:52:06

Excellent writeup. Thank you. One correction, Service request message is n ot sent encrypted; it is sent integrity protected, but NOT encrypted. See Clause 4.4.5 of 24.301, where the bullet says: unciphered, if it is any other initial NAS message (other than CP Service request which is sent partially ciphered).  Ciphering is turned on when the service request procedure is successful, which imu, is SMC mode command (step 7) if authentication occurs, or after DRBs are setup (step 10).

bhavya 2022-07-12 12:22:53

hi Netmanias, one small question , what is difference bwteen seesion ID and tunnel ID and is session ID stored any where .. this queary is with respect to diagram 7 above...

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